Nance - you have a lot of great recommendations here - many that add nutrition as well as great flavor :) Personally, if using starch or flour, I prefer potato or tapioca - not too fond of cornstarch any more, and I have yet to try the rice flour but think it's a great idea, too. (I also like the coconut or almond flour recommendation - they add a nice, unexpected flavor.) The one thing you want to remember when using any thickener is (forgive me if someone already mentioned this, I don't recall reading it) to mix it with cold water or milk prior to adding to your other ingredients / gravy / sauce. You will avoid lumps by doing so, and then stirring the mixture in slowly with a whisk.
The ground / grated veggies add a great flavor, too, but many people don't like the texture or the look of those vegetables; I don't mind...
Here's a tip for those times when you don't need a "quick fix" thickener - whenever I make chicken, lamb, pork, or beef with the bone in, I save the bones to make bone broth as a natural thickener (bones are what make glue and gelatin.) Sometimes I will remove the bones before cooking my meat / poultry and freeze (this is especially effective when bones are small or on a small portion of meat, as you can add to the package of frozen bones until you get enough to make a good broth), sometimes, as with roasted chicken, I remove the meat from the bones after roasting for an extra special tasty treat. Whatever method I choose initially, what I do with the bones is always the same... Put the bones and any other solids such as (grissle, fat, skin) in a slow cooker (or dutch oven of some type) and cover with water. If slow cooker, set on high and let the bones boil for as long as you like; I've actually boiled mine (adding water as necessary) for 3 days in the slow cooker (I will turn it down to low or even warm if I leave the house.) When you think it's cooked long enough (I cook mine until the bones literally fall apart or can be cut with a good scissors or meat cutter because I want the marrow in my broth), remove the bones and other solids, refrigerate or freeze (in pints or quarts - if freezing, I refrigerate first so that fat rises to the top and I can discard it), dependent on how quickly you will use the broth, and viola!, you have instant thickener that's loaded with flavor.
I too, hope your dinner worked out well for you. I'd be interested in hearing your thoughts about the bone broth tip. I try my best to use everything I can use rather than discarding, so have many processes such as this for many foods (citrus fruits, etc.)